140 EXHAUSTION OF SOILS. FALLOWING. 



unfruitful pasture-land, which, without manure, produces neither 

 wheat nor tobacco. From every acre of this land, there must 

 have been removed in the space of one hundred years at least 

 1200 Ibs. of alkalies, in leaves, grain, and straw; it became 

 unfruitful, therefore, because it was deprived of every particle of 

 alkali, that had been reduced to a state capable of being dis- 

 solved; and it would require to lie entirely fallow for a great 

 length of time, to regain its fertility. Almost all the cultivated 

 ground in Europe is somewhat in the same condition. That of 

 many of the West India islands has been also exhausted, by the 

 avarice of its former possessors ; who have left it in a state, which 

 renders the cultivation of Sugar much less profitable than formerly, 

 since the Canes cannot be grown without a large quantity of 

 manure. If the ashes of the Canes, which, after the juice has 

 been pressed from them, are burned, to heat the pans for boiling 

 down the fluid, were to be spread over the fields, the produc- 

 tiveness of the land would probably be much increased : and it 

 would be much preferable to give back to the soil the whole solid 

 matter of the Canes, which remains after the juice has been 

 pressed out from them, together with the leaves, &c. that are 

 stripped from them during their growth. Thus all the consti- 

 tuents of the tissues of the plant, which have been withdrawn 

 from the soil, would be restored to it ; and as the Canes would 

 thus be made to manure themselves (like the Vines already 

 mentioned, . 191, 192), the soil would thus be enabled to afford 

 successive crops, without the aid of any other manure. The 

 sugar would then be the only substance withdrawn from it ; and 

 this is probably formed, chiefly, if not entirely, at the expense of 

 carbon and water derived from the atmosphere. 



.207. It is not always necessary, however, that a field should 

 lie fallow, in order to render it capable of producing some parti- 

 cular kind of crop, the materials of which had been exhausted ; 

 for, if it be sown with some vegetable of an entirely different 

 kind, a profitable crop of this may be raised, whilst the land is 

 renewing itself for the other. The power of doing this depends 

 upon the nature of the ingredient which is deficient. It has been 

 formerly shown, that it is not the vegetable portion of the soil, 



